Multiple radiotelephone and telegraph circuit



April 16, 1935. E, R. TAYLOR 1,997,706

MULTIPLE RADIOTELEPHONE AND TELEGRAPH CIRCUIT Filed Sept. 20, 1952 Frequency ff 35 l Rec.

ZEC RF 0R PII/iin 2 Rec' d; @n .EIA l f w 2, .o Station ZJ-f7. 45 @legal/ala, Receiver INVENTOR E lylolr BY Wg ATTORNEY Lai Patented Apr. 16, 1935 PATENT l 1,997,7cc

MULTIPLE RADIo'rsLEPHoNE ANDV 'rstsoaarnzoiaouir Application, Septemberll, 1932, Serial No. .634,063

`1.9 Claims.

.This invention relatesto radiotelephone systems, and more particularly to arrangements vfor sending .telephone ortelegraph messages over radiotelephone" channels between a multiplicity of radio stations.

In operating a radiotelephone circuit such, vfor example', as may be used in a ship harboiyit is desirable tol transmit information not only between a ship and the shore but also-between ships or-between several ships andthe shore. It is also desirablein the 4interest of economy, ease oi operation, and simplicity of maintenance to operate all ship radiotransmitters at the same carrier frequency .and all ship radio receivers at a common carrier frequency whichis different from "the one transmitted from the ships. In accordance withthisv invention, circuit 'arrangements are provided whereby telephone or'telegraph messages maybe transmitted between any two'or more of therado stations withoutreadjustment of the carrier l-ifrequencies or causing objectionable singing or echoes. Y

' Asis Well known, a radio transmitter and radio receiver maybe connected by means of a combination oi .`fourwi`re'and two-wire circuits to a two-,wire .terminal at .a switching Vpoint where connections may be establishedbetween Athe radio channel and'various I'telephone or telegraph circuits. It is .also Well knownthatterminal amplifiers, voice-operated ydevices and other apparatusunderthe control of a technical 'operator maybe .associated with .thefour-wire circuit in such .a mannerithat echoes and singing, which might-becaused by radio orwire line unbalances, are e'tectively eliminated, andradiation by the radio transmitter of, signals received by the radio receiver is prevented. 11n accordance with the invention, interconnections .between the vradio transmitter, the .radio .receiver andthe voiceoperated devices of ,suchastation are provided, so .that the radio transmitter andthe radio receiver may..be.used.as a frequency'chan'ger and radio .repeater in communications between two or more of the other radio stations without interfering withthe normal operationof theinterconnectedimitsiin .communications ,between .the circuits connected at the switching .point and the distant radio stations.

Y .Arrangements are included .whereby the amount of energy .delivered bytheradioreceiver tothe radio transmitter .when .they are acting as avradio.rep.e.ate11may bei adjnstedby Ythe .technical operator when necessary, ,order toA .obtainV the desired .percentage of .modulation .and so that the radio repeater l.action may .be Vdisabled when mi. 25o-fa) its use .is undesirable on account of abnormal radio conditions ory because the vadditional publicity of re-radiationis' not desired. "Other arrangements are provided whereby'thetechnical operator may monitor 'transmission in both` vvor either Adnection and may Vcontrol the amounts of amplication and the sensitivities of the voiceoperated devices, and may cominunicatein either or both directions as desiredl Whereas static and other interference which is received by theradio'rceiveralong with'ithe desired signals is relradiat'e'dby the rado'transmitter when the 'systemis acting as 'a radiorepeater, such'static and interference is not `re radiated when signals from the twoewireline are being transmitted.' The invention may now be more fully understood from the following descriptionwhen read in connection with'the accempar'iying'V drawing, Figure 1 of which showsY thecircnit 'arrange'- ment for one 'terminal of "a radio Jsystemy embodying the invention which'acts `as the radio repeater, 'and Fig'. 210i which shows a circuit arrangement wlnch maybe used for oneor'more of -the other radio stations. Figs. lSand @show respectivelya telegraph transmitter and ya telegraph receiver which maybe substituted for 'the telephone transmitters and telephonereceivers, in Figs. 1 and 2 when'telegraphr operation is desired.

Referring to the drawing, Fig. 1 shows the cir-Y cuit arrangement of one end ofthe radiotelephone system' whichwill be called the shore station for 'descriptivepurposes." Fig. 2 'shows the circuit arrangementE of oneof the'radi 'stai tions to be communicated with, whichfis called a .shp station -for descriptivepurposes." It will be understood, of course, th'atthe'invehtion is not to `be-limited to a shipL'to-'shore radio` telephone system, 4

Referring to Fig-1, -SL designates the two-wire line Yconneotingthe shore stationto -theswitchboard. The V-twowire line SL A is 4connected through a hybrid coil HB1 to a transmitting path, TLi and a lreceiving path RL1,`being`-balancedby a suitablel network N1. The path TL1`v and the following parts of the trans'mittmgcrcuit include the transmitting volumeco'ntrol variable attenuator -FIVC,amp1ier TA, hybrid coil HB2,

transmitting path TLz, `.the normally ope'noonl- F tacts of relay TSS, transmitting path TL3 trans-v former .T1 and radioitransmitter ,RTL myIhe receiving. path includes radio receiver RRi, receiving path yR112;transformers-T2, 51's and-T4', -resist-Lance termination RTZ, receiving volume control att'e'nuv ator RVC, amplifier RA and receiving path RLi.

In order that when transmission is taking place over either the transmitting or receiving path the other path will be disabled, echo suppressor devices are associated with each path. The echo suppressor associated with the transmitting path TL1 comprises an amplifier-detector unit TAD, of well-known type, with its input connected through variable attenuator TSC to hybrid coil HB2 in conjugate relationship with transmitting path TL2, the output of amplifier TA being balanced by a suitable network N2. The output of the amplifier-detector unit TAD controls through master relay TM the relays TSS and TEHO for performing operations incident to the blocking or disabling operations whereby transmission is permitted in only one of the paths TL2 and RLi at a time. Normally, transmission path TLz is disabled by the back contacts of relay TSS, which short-circuits the conductors, and transmission from transmitting line TL1 to the radio transmitter cannot take place. Blocking means comprising transformer arrangements T3 and T4 are associated between receiving lines RL; and RL2. 'I'hese disabling means comprise transformer arrangements which are so connected as to be balanced when the contacts of relay TEHO are opened, thereby preventing transmission through the transformer arrangements. When the contacts of relay TEE-IO are closed, however, the transformer circuits instead of being balanced are, in effect, connected so as to be parallelaiding, thereby permitting transmission to take place readily. Normally, relay TEHO (which is controlled by the amplifier-detector TAD) is deenergized so that the receiving path is unblocked to permit transmission to take place from the radio receiver RRi to the two-wire line SL. The input of an amplifier-detector arrangement RAD is connected through receiving sensitivity control RSC and rresistance termination RTi to the secondary windings of transformer T4, so as to be effectively in series with the resistance termination RT2 in the receiving path RL1, and has in its output a relay RM, which when operated opens the control circuit from the amplifierdetector TAD to switching relays TSS and TEHO, thereby maintaining the transmitting path TL2 blocked and receiving path RL1 unblocked when signal currents are being received from the radio receiver RRi.

The operation of the apparatus so far described for signal transmission is as follows: Signal currents incoming over the two-wire circuit SL pass through the hybrid coil HB1 and through the amplifier TA. Some of the energy enters the amplifier-detector unit TAD and causes relays TM, TSS and TEHO to be energized. Relay TSS removes the short circuit from transmitting line TL2, while relay TEHO, by opening its contact, causes the transformer arrangement Ta and T4 to block the receiving path. In the meantime a part of the energy passes from hybrid coil HB2 through transmitting paths TL2 and TLs to radio transmitter RTi and is transmitted on carrier frequency F1. The receiving amplifier-detector RAD associated with the receiving path cannot be actuated to disturb the circuit condition now existing because the receiving path is disabled in the manner already described.

If in the normal condition of the circuit, signals are received over line section RLz from the radio receiver RR; which is tuned to carrier frequency F2. they pass through line RL; and the transformer arrangements T3 and T4. A part of the energy passes through receiving amplifier RA and hybrid coil HB1 to the two-Wire line SL. The remaining received energy passes through receiving sensitivity control RSC to the amplifierdetector RAD, to cause the operation of relay RM which opens the circuit controlled by the amplifier-detector unit TAD, thereby preventing energization of relays TSS and TEHO, so that the transmitting path is disabled and the receiving path remains unblocked so long as the signaling currents are being received.

The apparatus so far described relates to communication between the two-wire line SL and a ship station. The additional equipment and the circuits which are associated with the shore station in order to afford radio repeater action in communication between ship stations will not be described. Referring to Fig. 1, it will be seen that a by-pass is connected between the receiving and transmitting legs of the four-wire circuit, in order to by-pass the voice operated equipment and the two-wire line and convey energy from the radio receiver to the radio transmitter, eiltectively connecting them in cascade and establishing a radio repeater. 'I'he by-pass includes energy dividing circuit DC in the receiving path between transformers T2 and T3, by-pass line BYLl volume control attenuator BC, the normally open contacts of key BK, by-pass line BYLz, and the normally closed contacts of relay TSS. KeyBK is so arranged that when radio repeater action is not desired it may be left in the unoperated position shown and transmission path BYL1 is terminated in resistance termination RT3, and

transmission path BYLz is short-circuited, permitting normal operation in communication between radio stations and the two-wire terminal.

Radio repeater action may now be described: if key BK is operated and the voice-operated relays are in their normal positions, signals from the radio receiver RRi pass through transmission path RLz and transformer T2 to dividing circuit DC, where a part of the energy passes to transformer arrangements T3 and T4 and the remainder passes through transmission path BYLi. The latter is attenuated to the desired value by attenuator BC and passes through contacts of key BK and relay TSS, transmission path TLS and transformer T1 to the radio transmitter RT1, where they are re-radiated on the desired radio frequency. A part of the energy which passes into transformer arrangements Ta and T4 causes the operation of relay RM in a manner similar to that described above for communication between the two-wire line and a ship station, and the remainder passes to the twowire line SL. The operation of relay RM prevents echoes or other signals transmitted by the twowireline from causing operation o1' relay TSS and consequent mutilation of the repeated signals. When the echoes of the received signals have ceased, relay RM releases and normal conditions obtain.

If signals from the two-wire line are to be transmitted while key BK is in the operated positions and signals are not being received by the radio receiver, the apparatus and circuits function in the normal manner for such transmission as described above. The by-pass is disabled in this case by the operation of relay TSS which short-circuits transmission path BYL; shortly after it removes the short circuit from transmission path TL2. During the travel time of the armature of relay TSS (the time after the short circuit has been removed from transmission vpath 'ILz and before it is. appliedY to transmission path BYLz) transmission paths TL2, TLs and lBYLz are effectively connected in series but false operation of relay RM by energy passingfrom ltransmission path ,TLz through transmission path ,BYLa is prevented by the disabling action of transformer arrangements T3 and Ti since relay TEHO opens its contact at the same time that relay TSS removes its short circuit from transmission `path TLZ.

vApparatus and circuits are included in the shore station wherebythe technical operator may communicate with the ship stations or over the `twoewire line and may monitor transmission in either direction. The facilities whereby the technical operator at the shore station signals to the ships include operators transmitter OT1, key TBK, and transmission path TR, which is connected in multiple with transmitting volume control attenuator TVC. The facilities whereby he transmits over the two-,wire line include operators transmitter OT1, key TSK and transmission path TS, which is connected in multiple with the primary of transformer T3. Keys TRK and TSK in'their normal positions are arranged to hold open the paths from the operators trans mitter OT1. Signals received over the radio and the twowvire line may be monitored by the technical operator with apparatus and circuits which include transmission paths MR and MS, transformers T5 and Ts, keys MRK and MSK, and operatorsreceiver OR1. When key MBK is operated, monitoring is limited to signals ytransmitted over the radio, and when key MSK is operated, to signals transmitted into the two-wire line. When keys MBK and MSK are not operated, operators receiver OR1 is effectively in .series with transmission paths MR and MS, but

the transmission loss through transformers T5 and Ts issuciently large to prevent objectionable echoes being transmitted from one side of the four-wire circuit to the other through the monitoring circuit.

The apparatus and circuits employed at the shipstation may be of several Well-known types,

as, for example, those sho-wn in 2 which shows an antenna normally connected to radio receiver RRz which is arranged to receive carrier frequency F1, and the radio transmitter RTL, arranged to transmit carrier frequency F2. The antenna may be switched from the radio receiver RRZ to radio transmitter RT'Z in a well-known manner by relay AR which is controlledby key AK. The output of radio receiver RRZ is connected to operators receiver ORz and the input of radio transmitter RTg is connected to operators transmitter 0T2. Accordingly, the operator at thev ship station may normally receive signals transmitted on carrier frequency F1 and may transmit signals on carrier frequency F2 by oprating key AK which enables radio transmitter RTz and disables radio receiver RR2. The operation of the ship station is the same for ship-toshore and ship-to-ship communications.

The apparatus and the circuits described heretofore are designed primarily for telephone coinmunication but maybe readily adapted to telegraph communication by the substitution of well known `voice-frequency telegraph equipment Vfor the operators transmitter and receiver. For eX- ample, operators transmitters GTi and 0T2 may be replaced by the arrangement shown in Fig. 3 and operatorsreceiver ORror OR2 by the arrangement shown in Fig. 4. The operationof ora printer if printing telegraph operation were y desired.

It will Vbe obvious that the general .principles herein disclosed may be embodied in many other organizations widely different from those illus trated, without departing from the spirit of the invention as defined inthe following claims.

`What is claimed is:

i.,The method of two-way signaling between a plurality of stations which consists of generating signals in a ,certain frequency band at one station, transmitting the signals through a transmission mediurn to a repeater point, converting them into a second frequency band at said repeater point, transmitting the converted signals through a transmission medium and detecting them at a second station, in signaling in one direction between stations in one group; generatingsignals in the iirst frequency band at said second station, transmitting them .through a transmission medium to saidrepeater point, converting them into the second frequency band at said repeater point, transmitting the converted signals through a transmission medium and detecting them at said first station, in signaling in the other direction between stations of that group; generating signals in the first frequency band at a station of said group, transmitting them through a transmission medium to said .repeater point, detecting them .at said repeater point, and transmitting them without conversion over a second transmission medium to a distant station in another group, in signaling in one dif them, in signaling in the ,other direction between i a station in the first group and said station outside said group.

2. The method of two-way signaling between a plurality of stations which consists of generating signals in a certain frequency band at one station, transmitting the signals through a transmission mediurn to a second station, detecting them Vat said second station and transmitting them without .conversion over a second transmission medium to a third station, in signaling in one direction to said third station; converting signals in said iirst frequency band to signals in a second frequency band at said second station, transmitting the converted signals through av transmission medium and detecting them in signaling to afourth station; and transmitting signals without conversion from saidthird station over said second transmission to s aid second station, translating said signals to saidsecond frequency/.band at said ,secondsta- Cil tion, transmitting them through said first transmission medium and detecting them at said first station, in signaling in the other direction from said third station to said first station.

3. The method of two-Way signaling between aplurality of stations which consists of generating signals in a frequency band at one station, transmitting the signals through a certain transmission medium to a second station, detecting them at said second station and transmitting them Without conversion through a second medium to a third station, in signaling in one direction to said third station; simultaneously repeating said signals translated into asecond frequency band into a third transmission medium at said second station, transmitting the translated signals through said third transmission medium and detecting them, in signaling to a fourth station; and transmitting signals without conversion from said third station over said second transmission medium to said second station, translating said signals to said second frequency band at said second station, transmitting them through said transmission medium and detecting them at said first station, in signaling in the other direction from said third station to said first station.

4. The method of two-way signaling between a plurality of stations which consists of generating signals in a certain frequency band at one station, transmitting the signals through a. transmission mediurn to a repeater point, converting them into a second frequency band at said repeater point, transmitting the converted signals through a transmission medium and detecting them at a second station, in signaling in one direction between stations in one group; generating signals in the first frequency band at said second station, transmitting them through a transmission medium to said repeater point, converting them into said second frequency band at said repeater point, transmitting the converted signals through a transmission medium and detecting them at said first station, in signaling in the other direction between stations of that group; generating signals in the first frequency band at a station of said group, transmitting them through a transmission medium to said repeater point, detecting them at said repeater point, and transmittmg there without conversion over a second transmission medium to a distant station in another group, in signaling in one direction between stations of the first mentioned group and another station outside said group; and in transmitting signa-ls without conversion over said second transmitting medium in the opposite direction from the station outside said first mentioned group to said repeater point, converting said signals into said second frequency band at said repeater point, transmitting them from said repeater point through a transmission medium and detecting them, in signaling in the other direction between a station in the first group and said other station; and suppressing reaction between transmissions in the two directions between a station in said first group and said other station.

5. The method of two-way signaling between a plurality of stations which consists of generating signals in a certain frequency band at one station, transmitting the signals through a transmission medium to a second station, detecting them at said second station, and transmitting them without conversion over a second transmission medium to a third station, in signaling in one direction to said third station; converting signals in said first frequency band to signals in a second frequency band at said second station, transmitting the converted signals through a transmission medium and detecting them, in signaling to a. fourth station; transmitting signals without conversion from said third station over said second transmission medium to said second station, translating said signals to said second frequency band at said second station, transmitting them through said first transmission medium and detecting them at said first station, in signaling in the other direction from said third station to said first station; and suppressing reaction between the transmissions in the two directions between said first and third stations.

6. The method of two-way signaling between a plurality of stations which consists of generating signals in a frequency band at one station, transmitting the signals through a certain transmission medium to a second station, detecting them at said second station, and transmitting them without conversion over a second transmission medium to a third station, in signaling in one direction to said third station; simultaneously repeatng the signals translated into a second frequency band into a third transmission medium at said second station, transmitting the translated signals through said third transmission medium and detecting them, in signaling to a fourth station; transmitting signals without conversion from said third station over said second transmission medium to said second station, translating said signals to said second frequency band at said second station, transmitting them through said rst transmission medium and detecting them at said rst station, in signaling in the other direction from Said third station to said first station; and suppressing reaction between transmission in the two directions l between said first and third stations.

7. In a radio communicating system, a fourwire circuit comprising a transmitting path and a receiving path for connecting a radio transmitter and a radio receiver, respectively, to a two-wire terminal for the transmission of a signal band, and means for by-passing the two-wire terminal so that a part of the energy of full signal band width from the output of the radio receiver is fed into the radio transmitter without i passing through the two-Wire terminal.

8. In a radio communicating system; a fourwire circuit comprising a transmitting path and a receiving path for connecting a radio transmitter and a radio receiver, respectively, to a two-wire terminal for the transmission of a signal band, means for by-passing the two-wire terminal so that a part of the energy of full signal band width from the output of the receiver is fed into the radio transmitter without passing through the two-wire terminal, and means for preventing echoes of received energy which arise in the two-wire line from being transmitted by the radio transmitter.

9. In a radio communicating system, a fourwire circuit comprising a transmitting path and a receiving path for connecting a radio transmitter and a radio receiver, respectively, to a two-wire yterminal for the transmission of a single band, means for by-passing the two-wire terminal so that a part of the energy of full signal band width from the output of the radio receiver is fed into the radio transmitter Without passing through the two-wire terminal, and means for preventing energy from the output of the radio receiver from beingffed into the radio transmitter while energy from lthe two-wire terminal is being transmitted. v

1,0. In a radio communicating system, a fourwire circuit comprising a transmitting path and a receiving path for connecting a radio transmitter ,and a radio receiven' respectively, to a two-wire terminal, means for by-p-a'ssing'the twowire terminal so that a part ci the energy .from the output' of the radio receiver' is fed into the radio transmitter.without passing throughthe' two-wire terminal, means fori preventing echoes OAeceiVedenergy which arise in the two-wire line frombeing transmitted by the radio transmittenand means for preventing energy' from the output of the, radio receiver being fed into the` radio transmitter while energyfrom the twowire terminal is being transmitted.

,11, In, a radio communicating system, aifourwire circuit comprising artransmitting path and areceiving path for' connecting a radio vtrans-- mitter and a radio receiver, respectively,.to a twowireterminal forthe transmission of a signal band, means'for by-passingthe two-wire terminali sjothat a part of the energy of full signal bandwidth, ,from the outputotheradio receiver .is fed into the radio transmitterwithout passing through the two-wire terminal, and means for preventinggechoes of' energy which is fed from the` two-wire terminal tothe radio transmitter from being received by the radio receiver and re-transmitted by the radio transmitter.

12. In a radio communicating system, a fourwire circuit comprising a transmitting path and a receiving path for connecting a radio transmitter and a radio receiver, respectively, to a twowire terminal for the transmission of a signal band, means for by-passing the two-wire terminal so that a part of the energy of full signal band width from the output of the radio receiver is fed into the radio transmitter without passing through the two-wire terminal, and means whereby the amount of energy fed into the radio transmitter may be varied at will.

13. In a, radio communicating system, a twowire terminal, a radio transmitter, a radio receiver and means whereby the radio receiver may be connected to the two-wire terminal, an independent connection from the radio receiver to the radio transmitter, together with switching devices underthe control of energy to be transmitted from the two-wire terminal for disabling the independent connection from the radio receiver to the radio transmitter and for establishing a connection between the two-wire terminal and the radio transmitter.

14. In a radio communicating system, a twowire terminal, a radio transmitter, a radio receiver and means whereby the radio receiver may be connected to both the two-wire terminal and the radio transmitter, together with switching devices under the control of energy to be transmitted from the two-wire terminal for disabling the above connections to the radio receiver and for establishing a connection between the two-wire terminal and the radio transmitter, together with other switching devices under the control of energy received through the radio receiver for preventing the operation of the first mentioned switching devices under the control of energy to be transmitted from the two-wire terminal while energy is being received from the radio receiver.

15. In a radio communication system, a plurality of outlying radio stations each transmitting communication stationA from reacting on said transmitting equipment, and means at said central station to translate'the wave length at which it receivcs'to the'wave length at which it transmits to enable any outlyingstationto carry on two-way communication through theV central station asa repeater with any other outlying station.'

16. In .a radiol communication system, a plurality of outlying radiostations eachitransrnitting on the' same wavelength and each receiving onla different common wavelength, a central radio station having a transmitting channelincludinga radio transmitter to transmit on the i2 wavelength at which the outlying radio stations receive and a receiving channel including a radie .receiver receiving on the wave length at which the outlying radio stations transmit,

means to connect saidfchannels to a switching point to enable two-way communication to take place between any one of a plurality of communication stations and any of said outlying stations, said connecting means being arranged to prevent signals transmitted from said receiving equipment to a communication station from reacting on said transmitting equipment, and means to connect said receiving channel in tandem with said transmitting channel independently of the connection of said channels to said switching point, whereby the wave length received by said radio receiver will be translated to the wave length transmitted by said radio transmitter to enable any outlying station to carry on two-way communication through the central station as a repeater with any other outlying station.

17. In a radio communication system, a plurality of outlying radio stations each transmitting on the same wave length and each receiving on a different common wave length, a central radio station having a transmitting channel including a radio transmitter to transmit on the wave length at which the outlying radio stations receive and a receiving channel including a radio receiver receiving on the wave length at which the outlying radio stations transmit, a hybrid coil arrangement to connect said channels to a switching point to enable two-way communication to take place between any one of a plurality of communication stations and any of said outlying stations, and means to connect said radio receivingY channel in tandem with said radio transmitting channel independently of said hybrid coil whereby the wave length received by said radio receiver will be translated to the wave length transmitted by said radio transmitter to enable any outlying station to communicate through the central station as a repeater with any other outlying station.

18. In a radio communication system, a plurality of outlying radio stations comprising transmitting apparatus and receiving apparatus, a central radio station having a one-way transmitting channel and a one-way receiving channel, means to interconnect said channels with a transmission medium forming a two-way communication path to a communication station,

the connection being such that one channel is used solely for transmission in one direction over said path and the other channel is used solely for transmission in the opposite direction over said path, whereby said channels will operate on a four-wire basis to permit two-way signaling between a communication station associated with said central radio station and any of said outlying radio stations, additional means to so interconnect said channels that they will also operate in tandem so that the outlying radio stations can carry on two-way communication with each other through said central radio station acting as a repeater, the receiving apparatus of each outlying station being normally conditioned to receive and the frequencies being so assigned that when a communication station associated with the central station transmits, all outlying radio stations may receive signals and any outlying radio station may signal in the reverse direction to reply to the received signal.

19. In a radio communication system, a plurality of outlying radio stations comprising transmitting apparatus and receiving apparatus, a central radio station having a one-way transmitting channel and a one-way receiving channel, means to so interconnect said channels with a transmission medium forming a two-Way communication path to a communication station, the connection being such that one channel is used solely for transmission in one direction over said path and the other channel is used solely for transmission in the opposite direction over said path, whereby said channels will operate on a four-Wire basis to permit two-way signaling between a communication station associated with said central radio station and any of said outlying radio stations, additional means to so interconnect said channels that they will also operate in tandem so that said outlying radio stations can carry on two-way communication with each other through said central radio station acting as a repeater, the receiving apparatus of each outlying station being normally conditioned to receive, communication stations associated with the central oiice being also normally conditioned to receive, and the frequencies of the outlying radio stations and the central radio station being so assigned that when any station of the system transmits, regardless of whether the transmitting station is an outlying radio station or a communication station associated with said central radio station, all other stations of the system may receive the signals and any other station of the system may signal in the reverse direction to reply to the received signal. EDMUND R. TAYLOR. 

